Taking as reference the manufacturing of a coating placed at the aircraft tail. Said coating consists of a base piece constituted by a laminate named skin and by an assembly of pieces rigidizing said skin, and which are named essential pieces, such as rib fastenings, stringers, capstrips, etc.
The laminate constituting the skin is obtained by stacking several layers of composite materials, either manually or in an automatic machine. Likewise, different essential pieces are obtained: rib fastenings, stringers, capstrips, etc., which when joined together and together with the base skin form a complete coating.
Before carrying out the automatic or manual laminating, it is required to perform a compaction process of several layers of composite materials on a tool, also named cradle, in order to allow performing the correct stacking, also known as the taping or laminating, of the different layers constituting the skin. In the specification, for consistency in the terminology, the terms tool and taping are utilized. In the compaction process, a mould release agent is first applied on the skin manufacturing tool in order to avoid the skin piece from remaining attached thereto.
Then the curing of the mould release agent by applying heat is performed. The remainders of the cured mould release agent are cleaned from the tool and immediately after another layer of mould release agent is applied. Once the mould release agent is dried, a layer with adhesive properties is extended on the tool in the entire surface corresponding to the skin piece dimensions, for which the layer with adhesive properties should present at least slightly larger dimensions than said skin piece. The objective of this layer is to refill the pores that may persist on the uncovered face of the coating and thus leaving a completely smooth surface.
In order for the layer with adhesive properties to stay completely adhered to the tool, a first compaction wherein a vacuum paste is attached around the tool is carried out and next an aerator blanket formed by a separating film and an aerator fabric is extended along the same. The blanket is utilized for the vacuum to equally circulate throughout all points and must have dimensions larger than the compaction area of the skin piece.
Next, a plastic layer that is attached to the previous paste is extended, and all of that in such a way that in the plastic layer is coupled a vacuum valve which, connected to a vacuum rubber which in turn is connected to the corresponding compressor, in order to extract the air from the interior of the plastic bag wherewith the compaction process of the layer with adhesive properties previously mounted is performed.
Once the compaction has been performed for about 10 minutes, the compaction bag is lifted leaving the plastic joined to one of the tool sides and the aerator blanket is removed. Once the interior of the bag has been uncovered, all those composite material patterns that should be introduced in the preparation prior to the taping of the laminate are positioned where corresponds, due to mechanical and/or designing needs, as for example, areas that should incorporate rivets.
Next, a layer with conductive properties is mounted on the entire surface of the skin piece for providing electrical continuity to the same. This layer can present a pre-impregnated mesh-shaped configuration, in which case the protective paper incorporating said layer with conductive properties is left on the face opposite to the tool, i.e. facing upwards, and a new compaction is carried out. As the vacuum paste is already attached to the bag at one side of the tool, the aerator blanket must be extended again and the vacuum bag closed in order to next connect the vacuum valve to the compressor. The conductive layer can also present a pattern-shaped or any other geometry configuration, in which case it is positioned in the corresponding place and following the mounting specifications specified by the manufacturer and the compaction is carried out by applying the vacuum on the bag.
Once the patterns and/or the layer with conductive properties have been compacted for about 10 minutes, the compaction bag is lifted leaving the plastic joined to one of the tool sides and the aerator blanket is removed in order to then detach the protective paper from the layer with conductive properties and the cut of the same is carried out, if appropriate, according to the outline that the skin piece presents, for which the entire outline is fasten with duct tape. In certain coatings some sheets rigidizing certain areas are positioned, which are placed in those points where is needed more structural rigidity, as for example, the ribs abutting a coating piece with another one through the rib fastenings. Finally, said sheets are covered, if appropriate, with a new layer with adhesive properties with similar dimensions.
Finally, the aerator blanket is placed again and the bag is closed in order to subsequently apply vacuum and compact the last layers. Next, the taping of the skin on the tool is carried out. If the taping of the layers constituting the skin is carried out manually, the bag for compacting is removed after about 10 minutes as well as the aerator blanket, and the taping process is started. Since said process has several compactions, the steps wherein the aerator blanket is placed and the bag is closed are repeated in order to subsequently apply vacuum and compact the last layers, as well as removing the bag for compacting and the aerator blanket after about 10 minutes. If the taping process is produced in an automatic machine, the tool is kept connected to the compressor until entering into the tape winding machine whereby the piece constituting the coating skin is laminated on the layers previously compacted.
Accordingly, in the compaction process the plastic layer which together with the vacuum rubber constitutes a vacuum bag is utilized. This configuration determines that pricks or chinks may appear in the plastic causing the bag to lose the vacuum, wherewith it is required to search for the prick location in order to carry out its repairing, and in the case that multiple chinks or pricks occur, is necessary to remove the bag and place a new one.
In addition, once the described compaction process has been finished, the plastic bag is substituted when carrying out a new compaction process, in order to have a higher reliability in the process, which considerably increases the costs thereof besides generating residues from the plastic and vacuum paste utilized, which with the use deteriorates and requires its substitution, which equally determines a higher run time and costs in the compaction process. Besides the materials costs, logistic costs such as the transport of the supply staff and materials are also carried out, as well as the transport of the wasted materials for its recycling and the staff thereof, besides the environmental impact that this involves.